Suspension polymerization of vinyl aromatic monomers in the presence of unsaturated carboxylic acid

ABSTRACT

The production of polymer beads by a suspension polymerization process in which a vinyl aromatic monomer having a free-radical generating catalyst dissolved therein is suspended in an aqueous medium with the aid of from 0.2 to 1.0 per cent by weight, based on monomer, of a finely divided phosphate suspending agent and heated to cause the monomer to polymerize into polymer beads is improved by the addition to the suspension of at least about 0.0001 per cent by weight based on monomer of an Alpha , Beta ethylenically unsaturated carboxylic acid as sole extender. The process of the invention is especially applicable in the preparation of large polymer beads.

Unite States Patet 1 Wright [451 Aug. 28, 1973 [75] Inventor: Harold Austin Wright, Murrysville,

[73] Assignee: Sinclair-Koppers Company,

Pittsburgh, Pa.

[22] Filed: June 29, 1971 [21] Appl. N0.: 157,848

[52] US. Cl.260/93.5 W, 260/785 R, 260/88.l PC,

260/91.5 [51] Int. Cl. C08f l/ll, C08f 7/04 [58] Field of Search 260/935 W, 88.1 PC, 260/9l.5

[56] References Cited UNITED STATES PATENTS 3,647,773 3/1972 Ohe et a1. 260/935 W 2,652,392 9/1953 Hohenstein et a1. 260/935 W 2,687,408 8/1954 Grim 260/935 W 3,068,192 12/1962 White 260/935 W 3,449,311 6/1969 Lowell 260/935 W Primary Examiner-James A. Seidleck Att0rneyLewis J. Young et al.

[ 57] ABSTRACT The production of polymer beads by a suspension polymerization process in which a vinyl aromatic monomer having a free-radical generating catalyst dissolved therein is suspended in an aqueous medium with the aid of from 0.2 to 1.0 per cent by weight, based on monomer, of a finely divided phosphate suspending agent and heated to cause the monomer toA polymerize into polymer beads is improved by the addition to the suspension of at least about 0.0001 per cent by weight based on monomer of an a,B-ethylenically unsaturated carboxylic acid as sole extender. The process of the invention is especially applicable in the preparation of large polymer beads.

4 Claims, 1 Drawing Figure SUSPENSION POLYMERIZATION OF VINYL AROMATIC MONOMERS IN THE PRESENCE OF UNSATURATEI) CARBOXYLIC ACID BACKGROUND OF THE INVENTION Free-radical initiators, particularly peroxidic initiators such as benzoyl peroxide, are commonly used as the primary initiator, or catalyst, in the suspension polymerization of vinyl aromatic monomers such as styrene. These initiators, being predominantly oil soluble and water insoluble, are believed to react within the monomer droplets in suspension to cause the polymerization in the following manner:

ROOR "it" 2R0- R M ROM-i ROMM- etc.

Grim U.S. Pat. 2,673,194, describes the suspension polymerization of vinyl aromatic monomers, whereby an oily monomer is suspended as droplets in an aqueous medium and polymer beads or particles are produced by the use of an oil-soluble polymerization catalyst, such as benzoyl peroxide. The suspending system of Grim patent is comprised of finely divided, difficultly water-soluble phosphates, and an anionic surfaceactive agent which serves as an extender. As used in this art, compounds which act to increase the ability of the finely divided phosphate dispersant to stabilize suspensions are termed extenders. The extenders increase the ability of the phosphate dispersant to maintain stable suspensions with a greater proportion of monomer and/or polymer in the suspension polymerization medium. Among the extenders listed by Grim are: sodium dodecylbenzene sulfonate, sodium tetradecyl sulfate, potassium stearate, and long chain alkyl sulfonates.

The suspension systems such as that of Grim produce polymer beads having a broad particle size distribution. The individual beads produced in suspension may range in diameter from less than 300 microns to above 2,000 microns with the average bead diameter being dependent upon the amount of suspending agent and extender present in the system. The average bead diameter can be controlled to some extent by varying the parameters of the system such as the ratio of suspending agent to extender or the ratio of suspending agent and extender to monomer. Although the average diameter size is changed through such variations, nevertheless, beads will be produced whose particle size range is broad.

For commercial reasons, it is highly desirable in this art to control the average particle size range within relatively narrow limits. This is especially true where the polymer beads are to be impregnated with a volatile expanding agent to produce polymer beads which will, upon heating, expand, e.g., in a mold, to fill the mold cavity and produce fused, expanded polymer articles.

One of the major uses of expandable polymer beads, particularly polystyrene beads, which are produced commercially by suspension polymerization, is in insulation applications such as insulation board. In manufacturing insulation board, it is common to mold a large (e.g. 4 ft. X 8 ft. X 20 ft.) billet of expanded polystyrene and subsequently cut the billet into slabs one or two inches thick for ultimate use as an insulation board. In preparing the large billets from expandable polymer beads, the beads are first preexpanded to form nonfused, partially expanded beads having a bulk density of from 0.8-1 .2 pounds per cubic foot. The partially expanded beads are then charged to the billet mold, and

heat, usually in the form of steam, is applied to fully expand the beads whereby they fill the mold, fuse, and fonn the billet.

1n the billet-molding application, it is especially critical that the expandable polymer beads be relatively large and substantially spherical.

1f the beads are too small, then the expandable beads at the outer surface of the billet mold will fuse too soon, thereby excluding steam from the center of the mold. The resulting billet, therefore, has a center of unfused, expanded beads which is, of course, highly undesirable since any unfused portion of the billet is useless.

Hohenstein et al, in U. S. Pat. No. 2,652,392, reduced the amount of small particle-size beads formed by adding a water-soluble persulfate-as extender for the calcium phosphate stabilizer.

I have shown in my copending application, Ser. No. 868,286, filed Oct. 14, 1969, now U.S. Pat. 3,631,014 that narrow distribution of bead sizes larger than 300 microns in diameter can be produced by the addition of at least 0.0003 per cent by weight based on monomer of sodium bisulfite as sole extender for the phosphate.

l have also shown in my copending application, Ser. No. 48,418,. filed June 22, 1970, now U.S. Pat. 3,649,610 that narrow distribution of bead sizes larger than 750 microns in diameter can be produced by the addition of at least 0.01 per cent by weight based on monomer of certain terminal vicinal hydroxy-keto compounds as extender for the phosphate.

SUMMARY OF THE INVENTION 1 have now discovered another class of compounds, namely a,B-unsaturated carboxylic acids, which when used as extenders for the difficultly water-soluble phosphate allow the preparation of polymer beads by the suspension polymerization of a vinyl aromatic monomer in an aqueous system containing the phosphate. The phosphate is preferrably used in amounts between 0.2 and 1.0 per cent by weight based on monomer. The extenders may be any of the a,B-unsaturated mono-, di-, or tricarboxylic acids and are used in amounts between 0.0001 and 1.0 per cent by weight based on monomer and such that the ratio of the phosphate to the acid is between 10 to l and 1,000 to 1. It is possible, by selection of the proper acid extender in the appropriate ratios to the phosphate to obtain by the method of the present invention, polymer beads having a narrow distribution of particle sizes greater than about 1200 microns in diameter, e.g. 1,200-3,400 microns.

DESCRIPTION OF THE DRAWING The drawing is a bar graph comparing a typical bead size distribution obtained in accordance with the process of the invention and a distribution obtained using a conventional polymerization system of tricalcium phosphate and sodium dodecylbenzene sulfonate.

DETAILED DESCRIPTION This invention is applicable in the suspension polymerization of vinyl aromatic monomers such as styrene, alpha-methyl styrene, monoand dichloro styrene, as well as the copolymerization of vinyl aromatic monomers with such monomers as divinylbenzene, alkyl acrylates, diallyl esters of dibasic, aliphatic or aromatic acids, butadjene, and other polymers capable of further polymerization such as styrene-butadiene, styrene-isoprene, and polybutadiene rubbers.

The finely divided, difficultly water-soluble phosphates useful as dispersing agents in the practice of this invention are conventional and are those described, for example, in Grim Pat. No. 2,673,194. They include those finely divided phosphates difi'icultly soluble in water containing for each phosphate group at least three equivalents of a metal, the carbonate of which is only slightly soluble in water, e.g., tricalcium phosphate, hydroxy-apatite, magnesium phosphate, etc. Advantageously, the amount of phosphate to be employed in this invention ranges from about 0.20 to 1.0 per cent by weight based on monomer. The average particle size of polymer beads produced in the suspension polymerization depends primarily upon the total amount of phosphate suspending agent; for example, suspension with larger amounts of phosphate suspending agent yields beads of a smaller average particle size.

The use of the novel extenders, i.e. a,fl-unsaturated carboxylic acid compounds of this invention as sole extender reduces the proportion of polymer particles produced that have sizes that deviate substantially from the mean particle size of the polymer beads produced. Surprisingly, the extenders of this invention allow the production of large, essentially spherical, beads having few, if any, out-of-round beads. it had been the experience heretofore that when large bead sizes were obtained, the beads produced were not spherical. Surprisingly, also the bead size distribution of the heads is confined within selected narrow limits by providing an extender in accordance'with this invention for the difficultly water-soluble phosphate comprising an a,B-unsaturated mono-, di, or tricarboxylic acid. The acid compound is added as the sole extender in the system.

Suitable extenders found to be effective in accordance with the invention are the a,B-unsaturated monodi-, and tricarboxylic acids. Examples of such acids found suitable are acrylic, methacrylic, crotonic sorbic, maleic, fumaric, citraconic, mesaconic, itaconic, and aconitic acids.

The acids are effective in amounts between 0.0001 and 1.0 per cent by weight based on monomer. The amount of extender used depends upon the amount of phosphate and the ratio of phosphate to acid should be between to 1 and 1000 to 1. The preferred ratio of phosphate to extender is between to l and 500 to 1. Depending on the acid used, the ratio of phosphate to acid may be higher or lower. For example, itaconic and acrylic acids allowed the suspension to fail at ratios below 5 to 1, but aconitic acid maintains suspension at a ratio as low as 1 to 1. Similarly, suspensions have been maintained with itaconic acid at a ratio of 10,000 to 1, whereas both acrylic and methacrylic acids allowed failure of suspension at 10,000 to 1 ratio.

The process of the invention may be used with monomer to water ratios which vary from about 0.3 to 1.5 parts by weight monomer per 1.0 part by weight water. The invention is especially valuable in that generally high monomer to water ratios are used, and a higher proportion of monomer in the suspension system is, of course, preferred from an economic standpoint.

The time and temperature cycles for the polymerization may be those conventionally employed. Conveniently, the cycle described in the Grim patent above, or the two-stage temperature cycle described in D'A- lelio U.S. Pat. 2,692,260 is employed.

The free-radical initiating catalysts which are added to the suspension system are the conventional oilsoluble (monomer-soluble) oxidation catalysts such as organic peroxides, e.g., benzoyl peroxide and t-butyl perbenzoate. Other free-radical producing catalysts that may be used in the invention include azobisisobutyronitrile. Conveniently, conventional amounts of such catalysts are used in the invention.

This invention is further illustrated by, but is not intended to be limited to, the following examples wherein parts are parts by weight unless otherwise indicated.

EXAMPLE 1 To a l2-ounce, crown-capped bottle was added 100 parts of water, 0.5 part of the dispersing agent, tricalcium phosphate, 0.005 part aconitic acid as extender, 030 part of the catalyst comprising 0.25 part of benzoyl peroxide and 0.05 part of t-butyl perbenzoate, and 100 parts of styrene monomer. The suspension was tumbled end-over-end in a heated oil bath at C. for 7 hours. The suspension was then cooled and acidified with hydrochloric acid to a pH of about 1.0 to dissolve the phosphate. The beads were separated by centrifuge, washed with water, and air dried. The beads were screened into portions. The screen analysis, U. 8. Standard Sieve, in per cent by weight of polymer beads retained on each size screen, is as follows:

Weight Percent Screen No Polymer Retaine 6 7.0 8 44.8 10 19.8 1 6 23 .2 20 2 .0 25 0.9 40 0.3 Pan It should be noted that the weight per cent polymer recorded in the screen analysis does not add up to per cent. The reason for this is that the weights are based on 100 parts monomer. Thus the total percentage represents the per cent yield of polymer based on monomer and does not represent a percentage of the total polymer beads formed. All screen analyses in these examples are reported in the same manner.

EXAMPLE [I So that a comparison could be made of the product of the invention with the product made by the use of an extender such as described in Grim U.S. Pat. No. 2,673,194, there were added to a reactor equipped with a two-bladed impeller, 42 parts of water containing 0.1316 part of the suspending system consisting of 0.131 part of tricalcium phosphate and 0.0006 part of sodium dodecylbenzene sulfonate (Nacconol NRSF), and 58 parts of styrene monomer having dissolved therein 0.171 part of the catalyst comprising 0.145 part benzoyl peroxide and 0.026 part t-butyl perbenzoate. The suspension was agitated at 68 rpm, and heated to 90C., which took 60 minutes. The suspension was maintained at 90C. for 365 minutes after which it was cooled and acidified with HCl to a pH of about 1.0 to dissolve the phosphate. The beads were separated by centrifuge, washed with water and air dried. The beads were screened. The screen analysis, U. S. Standard Sieve, is as follows:

TABLE 1 Weight per- Weight cent phospercent Screen analysis (No). wt. percent phate (on acid (on Phosphate/ Run No. Acid monomer) monomer) acid ratio 10 10 20 25 40 Pan I-1 Acrylic 1.0 0.004 250:1 56.5 33.2 3.3 0.4 Nil 1-2 Methacrylic 0.4 0.020 20:1 72.0 21.9 3.7 0.6 0.2 Nil {-3 Sorbic 0.4 0.020 20:1 39.5 7.9 0.0 0.3 0.1 x11 H Maleic 0.5 0.0005 1,000:1 7.0 31.3 20.4 10.7 10.0 0.3 1-5 Funiaric 0.3 0.0003 1,000:1 72.2 23.4 2.0 0.3 Nil 10 Citracnic 0.5 0.0005 1,000:1 4.0 30.7 40.1 12.0 11.5 0.2 1-7 Mesaconic 0.8 0.0008 1.0001 43.5 44.8 3.0 0.0 0.3 0.2 1-3 Itaconic 0.2 0.0002 1,0001 84.8 11.4 1.5 0.4 0.1 x11 I-9 Aconitic 0.7 0.007 1001 10.4 01.2 14.5 0.3 5.2 0.1

S N P figgf g suspension polymerized by the method of Example I. g e I The screen analysis of the resulting polymer beads is 16 I 5 shown in Table I. 3.4 12.1 24.1 249 EXAMPLE IV 8 In order to illustrate the applicable range of the ratio pan 8.4 20 of phosphate to carboxylic acid extender, a series of The screen analyses obtained in Examples 1 and I1 ar graphically illustrated in the drawing. The polymerization by the method of the invention in the presence of aconitic acid produces a bead diameter size range which is extremely narrow. The yield of product having polymerizations were run wherein 1 per cent phosphate was added to each of a series of bottles and the amounts of the indicated acid shown in Table 11 were added to vary the ratio. The remainder of the conditions (monomer, catalyst, temperature and time) were TABLE 11 Weight mr- Weight cent [1 mspercent. 5111171511li1l7llySlS(N0.), W1. prim-.111.

plinth (on acid (on l'liospllntn/ A Run A 0 Acid monomer) monomer) maid ratio 10 11'] 20 25 10 lnn II-1 Itaconlc... 1.0 0. 0001 10, 000:] 0. 8 3. 2 18.0 20. 8 47. 4 '1. 1 11-2 do 1.0 0. 0005 2.00021 Nil 0.4 0.0 1.2 31.3 04.0 11-3 do 1.0 0.001 1,00021 Nil 3.2 10.4 20. 0 42.8 13.4 114 .00 1.0 0.005 200:1 0 .9 31.3 31.6 10.0 13.4 10.. 11-5.. .(10 1.0 0.010 10011 3.6 47.3 17.2 7.4 10.8 11.0 11-6.. do 2.- 1. O 0.050 20:1 2.0 20. 0 13.4 8. 0 25. 5 2S. 0 11-7 .d0 1.0 0.10 10:1 0.7 14.5 14.2 0.8 34.2 24.7 118 do 1. 0 0. 20 5:1 Lost suspension 11-9 do. 1. 0 1. 0 1:1 Lost suspension 11-10... Acrylic 1. 0 0.0001 10, 000:1 Lost suspension 11-11"... do 1. 0 0.001 1, 00011 Lost suspension 1I12 do 1. 0 0. 010 100:1 3. 9 47. 6 2S. 5 0. 3 9.1 0.4 11-13... do 1. 0 0.050 20:1 0. 6 8. 5 23.0 16.1 40. 9 10.3 11-14... do..- 1.0 0.10 1011 0.5 4.1 15.1 13.1 39.7 24.8 1115 ..do 1. 0 1. 0 1:1 Lost suspension 11-16-.. Aconitic 1.0 0.001 1,000:1 Nil 0.5 1.8 3.1 50.9 41.6 11-17 do s 1. 0 O. 010 100:1 0. 4 32. 5 35. 8 10. 5 16. O 3. 0 11-18 do 1. 0 0. 050 20:1 Nil 2.1 15. 4 16. 7 4-4.1 30. 0 11-19 do 1. 0 0.10 10:1 13. 3 30. 2 3. 2 3. 8 25. 3 22. 3 1120 lo 1. 0 1. 0 1:1 Nil 18. 2 28. 5 12. 9 30. 4 S, 7

diameter greater than 1,200 microns obtained by the method of the invention was almost 95 per cent of monomer charged. The yield of product obtained by using a sodium dodecylbenzene sulfonate extender with the tricalcium phosphate suspension system was, in the desirable particle size, only 0.3 per cent weight of monomer chargedand the remaining 99.7 per cent by weight has a broaddistribution of sizes ranging from 300 to 1,200 microns.

EXAMPLE 111 To illustrate the general applicability of unsaturated carboxylic acids as extenders for tricalcium phosphate in the suspension polymerization of styrene, to each of a series of 12-ounce crown-capped bottles was added 100 parts of water, 0.30 part of the catalyst comprising 0.25 part of benzoylperoxide and 0.05 part of t-butyl perbenzoate, 100 parts of styrene, and the amounts of tricalcium phosphate as dispersing agent and the amounts of the indicated carboxylic acid shown in Table I. The bottleswere then capped and the systems EXAMPLE V To illustrate the known effect of phosphate concentration on the average bead diameter size the following series of polymerizations were carried out using the method and conditions of Example I while varying the acid extender, the phosphate concentration and the ratio of phosphate to acid. The results are shown in Table III.

TABLE III Weight percent Screen analysis (Nd). wt. percent 10 2 Pan Weight percent phosphate (on acid (on Phosphate/ monomer) monomer) acid ratio Acid Run No.

sQo2151823821n 937841 1 7 000 1 1 7 J. 4 9 93 19 NN OOARU 5188441963312181463 mmm7 nu7oc321920mm16 w mn nmmn m um nm 6 2 NLNQU MBIG QQU HO m mw mmmmmmmmmmmmmm mmmmmmmwmammmmmmmmm 086432076540860 4 74 LQQQQQ QQQQLQQLQQ QQ III1 Itacom'c it can be seen that the average bead size increases as divided, difficultly water-soluble phosphate, the imthe concentration of phosphate decreases. The data provement for producing a narrow distribution of bead also emphasizes the fact that various average bead sizes diameter sizes which comprises adding to the suspenand varying distributions of bead diameter sizes can be sion as sole extender a compound selected from the obtained by the proper selection of phosphate concengroup consisting of acrylic acid, methacrylic acid, crotration, extender, and phosphate to acid ratio. The 0ptonic acid, sorbic acid, maleic aci fumaric acid, mestimum concentration and ratio of phosphate suspendaconic acid, citraconic acid, itaconic acid, and aconitic ing agent to acid extender to yield a particular range of head sizes varies with the extender employed and may be determined by experimentation similar to that represented in Table III.

eO l .w .5 wm mm rm n n e m 0m m e P m m m m we MW e e la 0 0 DC Or. a u W m W m. M Ma m 0 m an we m Dun m sb s O, .l .mS n ew mam: a O flm H .000 h a o d s.mwm w n in 1d 10 l t emm a c e n o .m a m a m mo l mv. m t. h c i o a 5 fi eman .DWmS -mS S m o w. sd sD. n hm flw m em uukn. me o w O or. a p mdi e d r m lpu .pm D. nwm ww m e .l ib 0 mm mrmfi n T c r o n s m .m mw 2 3 4.m acrt Uc M t What is claimed is: 1. In a process for producing polymer beads by polymerizing a vinyl aromatic monomer selected from the group consisting of styrene, alpha-methylstyrene, monochlorostyrene and dichlorostyrene, with an oilsoluble, free-radical generating catalyst in an aqueous d vbm perbenzoate suspension under polymerizing conditions, where the suspension is stabilized by the presence of from 0.20 to l 0 per cent by weight based on monomer of a finely 

2. The process of claim 1 wherein said polymerization produces polymer beads having an average particle size greater than 1,200 microns.
 3. The process of claim 1 wherein said monomer is styrene and said catalyst comprises benzoyl peroxide and t-butyl perbenzoate.
 4. The process of claim 1 wherein said phosphate is tricalcium phosphate. 